1. Field
An embodiment of the present invention relates to a illumination optical apparatus using a reflection type original plate such as a reflective mask, exposure apparatus, and a device manufacturing method. More particularly, the present invention relates to exposure apparatus used in manufacturing devices such as semiconductor devices, imaging devices, liquid crystal display devices, and thin-film magnetic heads by lithography.
2. Description of the Related Art
The conventional exposure apparatus used in manufacturing the semiconductor devices and others is configured to project and transfer a circuit pattern formed on a mask (reticle), onto a photosensitive substrate (e.g., a wafer) through a projection optical system. The photosensitive substrate is coated with a resist, and the resist is exposed to light by projection exposure through the projection optical system, thereby forming a resist pattern corresponding to the mask pattern. The resolving power of exposure apparatus is dependent on the wavelength of exposure light and the numerical aperture of the projection optical system.
Specifically, in order to increase the resolving power of exposure apparatus, it is necessary to decrease the wavelength of exposure light and increase the numerical aperture of the projection optical system. In general, it is difficult in terms of optical design to increase the numerical aperture of the projection optical system beyond a certain value, and it is thus necessary to decrease the wavelength of exposure light to a shorter wavelength. Therefore, the technique of EUVL (Extreme UltraViolet Lithography) is drawing attention as a next-generation exposure method of semiconductor patterning (exposure apparatus).
The EUVL exposure apparatus uses the EUV (Extreme UltraViolet) light having the wavelength in the range of about 5 to 50 nm, when compared with the conventional exposure methods using the KrF excimer laser light at the wavelength of 248 nm and the ArF excimer laser light at the wavelength of 193 nm. When the EUV light is used as exposure light, there is no available optical material that can transmit the light. For this reason, the EUVL exposure apparatus has to use a reflection type optical integrator, a reflection type mask (in general, a reflection type original plate), and a reflection type projection optical system (see U.S. Pat. No. 6,452,661)